Exploring the Kilometer Deep Ice in Korolev Crater

Korolev crater’s domed ice deposit as seen from an oblique perspective. View generated from multiple images taken from the ESA Mars Express orbiter in late 2018. - Credit: ESA/DLR/FU Berlin

Establishing a Mars in situ resource utilization (ISRU) system to extract and process water will be extremely challenging. Aside from the challenges of power, heat, communications, and landing, the system will have to extract water from the environment and process it into a clean, usable product. Three potential sources of water a system like this may use include the atmosphere, hydrated soil (water trapped within soil), and ice/glaciers. Each of these sources may be at different locations with differing difficulties in extracting them. Surface ice deposits represent an appealing option because many of their characteristics can be determined before the system arrives, reducing risks. Once such surface ice deposit includes the massive ice deposit in Korolev crater.

Korolev crater is an 81.4 km diameter impact crater located near the Martian north pole (72.7°N, 164.5°E). Unusually, year round water ice is located within the crater even though it is at a latitude further south than the perennial ice stability line (approximately 74°N). The ESA Mars Express orbiter recently captured several high detail images of Korolev, offering never before seen views of the crater.

Many studies have investigated the Martian polar ice, having established that the Martian north pole is covered by a large layered deposit of relatively pure water ice [Howard et al., 1932; Malin and Edget, 2001; Phillips et al., 2008; Grima et al., 2009]. Studies have found that his ice formed mostly through deposition [Holt et al., 2010; Smith and Hold, 2010; Brothers et al., 2013; Smit et al., 2013], the process of water vapor freezing and being deposited on top of previously frozen ice. This means that these glaciers are stable within the current Martian environment, and did not likely form as a result of regional erosion of the glacier. This is important and relates to Korolev crater because it provides evidence for how ice is able to exists within the crater [Brothers et al., 2016].

Korolev crater in relation to the Martian north pole. Captured from the NASA Viking orbiter in 1998 - Credit: NASA/JPL/USGS

Korolev contains a domed ice deposit that is up to 1.8 km thick and contains between 1,400 and 3,500 km3 of water ice [Brothers et al., 2016]. It’s surface slopes dramatically down on the southern side of the crater (over 1 km lower than the peak) [Armstrong et al., 2005]. The crater walls extend several hundred meters above the ice surface, allowing the crater to act as a natural cold trap. Air moving over the ice cools down and sinks down into the crater creating a layer of cold air that acts as insulation between the cold ice and the warmer air around the crater. This cold trap is thought to be the driver behind the deposition process that allows the ice to exist.

Elevation plot across Korolev crater, where the southern-most portion of the crater is over 1 km lower than the northern regions. Bottom right shows a map of thermal regions where Cd refers to the southern cold material and Ct to the northern warm material - Credit: Armstrong et al., Figure 3, 2005

Radar data from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument has been used to peer into Korolev’s ice deposit (as shown below), providing evidence of its structure and history. Since the ice deposit’s shape is asymmetrical and domed shaped, it likely formed in place recently (5 million years ago or less) as opposed to being a remnant from a regional ice sheet extending from the pole [Brothers et al., 2016].

3D model of Korolev crater built from radar results from MRO’s SHARAD instrument. The distance from the top to the estimated bottom is about 1.8 km. - Credit: Brothers et al., Figure 4, 2016

Korolev’s structure and history are relevant to space resources because it increases our understanding of the crater’s ice, which not only could host evidence of life, but could also be a source of water for future missions. The ice deposition process is extremely slow, but it provides a natural example for how water can be extracted from the Martian atmosphere and stored in a relatively stable fashion. The current Martian climate allows the Korolev ice to exist, however, changes to the climate can impact this and cause it to change size.